David M. Ford - US grants

The self- and directed- assembly of colloidal (nano- to micro- scale) particles into structures within materials and devices is an emerging paradigm with wide-ranging technological impact. However, the ability to create a target structure with an acceptably small level of defects is still lacking; systems too easily become dynamically arrested in undesired disordered, or defect-rich, states. Our research will synergistically combine recent advances in digital microscopic imaging techniques and free energy calculation methods to address this problem. Emerging microscopic imaging tools, including techniques such as confocal and total internal reflectance, provide unprecedented high-resolution, real-time, three-dimensional visualizations of colloidal assembly processes. The key is to mine the tremendous amount of digital data produced in these experiments to identify successful pathways to particle assembly. Theoreticians have traditionally approached such problems using the energy landscape (EL) paradigm, wherein one maps data from the high-dimensional configuration space (of order N, the number of particles in the system) to an EL in a low-dimensional set of key descriptors. This EL is the quantity of direct relevance to engineering of the process of interest; it contains the information (peaks, valleys, saddles) to quantify the equilibrium states and transition rates between them. In this research we will (1) develop a close coupling methodology between digital optical microscopy experiments and particle-based simulation to compare measured and predicted ELs, and (2) use the resulting ELs to engineer (design, control, optimize) two applications: the self-assembly of photonic crystals and operation of electronic nanowire devices.

Particles with sizes on the order of nanometers to micrometers immersed in fluid, commonly called colloids, can serve as the building blocks of interesting new products. Examples include photonic band gap materials (e.g. for computers that operate with light instead of electrons) and dynamically reconfigurable nanowires (e.g. for tunable RF devices). Under certain conditions the colloidal particles will spontaneously assemble into such useful materials, or they can be induced to do so through the application of external stimuli such as electric fields or temperature gradients. However, the pathways to creating desired structures with acceptably low levels of defects are not well understood. This research employs a combination of modern digital imaging techniques and theoretical tools from the field of statistical mechanics to measure, quantify, and control the assembly process. We will develop knowledge of engineered pathways to low-defect structured particulate materials that can be systematically implemented in the manufacturing processes of the future. Furthermore, we will use the rich visual data generated in experiments (e.g. images, videos), simulations (e.g. renderings, animations), and analyses (e.g. dynamic, multi-dimensional plots) to provide intuitive educational experiences for students at all levels (K-postgraduate) and in outreach programs to the general public.

1033179
Ford

This project provides funding for the purchase of a 32-processor, 192-core computer cluster for research in molecular and materials modeling in the Chemical Engineering Department at the University of Massachusett, Amherst.

Intellectual Merit: This computing facility allows the study of large model systems across multiple length and time scales, as well as systematic parametric analyses using a range of modeling techniques including molecular computer simulation and quantum chemistry. The equipment will serve the computation needs of at least seven research projects in the groups of five faculty members. David Ford's group will use the cluster for classical density functional theory calculations on solid-fluid equilibrium and also for stochastic modeling of colloidal self-assembly processes. Peter Monson's group will use the new facilities for research projects on the dynamics of fluids confined in porous materials. Dimitrios Maroudas' group will use the equipment for their research on multiscale modeling related to the surface engineering of metals and semiconductors and plasma processing of carbon nanostructures. Furthermore, several collaborative projects across the groups will be supported. T.J. (Lakis) Mountziaris works with Maroudas on modeling the doping and synthesis of core/shell semiconductor nanocrystals, while Scott Auerbach works with Monson to model the self-assembly of ordered nanoporous materials, specifically zeolites.

Broader Impact: A commonality among the research projects to be supported by the new computing facilities is fundamental research in molecular and materials modeling in areas where there is a close connection with practical application. As an example, the development of new types of porous materials with properties tailored for specific applications is a major area of research throughout the world. Understanding of how the collective behavior of adsorbed
molecules is influenced by the microstructure of the porous material can contribute significantly in this effort. The investigators have reached the point where adsorption experiments can be accompanied by a much more sophisticated understanding of the structure. Monson's projects in this area could provide a foundation for new approaches to the characterization of porous materials. The range of potential impact extends across the range of applications of porous materials. Similar connections to application exist for all of the fundamental research projects to be impacted by the new facilities.

Research in the department has consistently had a strong educational component through the involvement of graduate students, postdoctoral scholars and undergraduates. The equipment requested will be used by 20 graduate students and 6 postdoctoral researchers, as well as undergraduates engaged in independent study projects. The junior researchers involved will learn important techniques in parallel computation for engineering applications. The faculty involved have an established record of bringing molecular and materials modeling into the Chemical Engineering curriculum and these activities will be supported by the new facilities.

A mix of financially needy community college transfer students and beginning graduate students including those in the Northeast Alliance for Graduate Education and the Professoriate majoring in Computer Science, Computer Systems and Chemical, Civil, Electrical, Industrial and Mechanical Engineering are receiving annual scholarships of $8,000. A total of twenty two students, approximately eighteen of whom are undergraduates receive support for two years while three or four graduate students receive one year support with the possibility of a second year. In many cases, the graduate students are those who need some additional studies beyond those taken as an undergraduate to qualify for full acceptance into a graduate program. The project builds on previous CSEMS and S-STEM awards.

The assembly of colloidal nano- or micro-particles into perfectly ordered periodic structures provides a basis for manufacturing photonic band gap materials and other multi-scale meta-materials with unique electric, magnetic, and optical properties. Although proof-of-concept materials have been made in laboratories to verify their amazing properties, no existing process is yet sufficiently controllable, scalable, and robust for high-throughput manufacturing to enable commercial applications. The fundamental limitation to assembling colloidal components into ordered structures is the complex interplay of thermal motion, interparticle interactions, and external fields that lead to defect-rich and often arrested states. We propose a new approach to the meta-material assembly problem that combines expertise from four separate scientific fields that traditionally have had minimal interaction. Mathematical models of the colloidal systems, represented as free energy landscapes (FELs) in a few key variables that characterize the state of the assembly process, will be constructed using data from advanced microscopic imaging and analysis tools. The FELs will in turn be used as input to rigorous process control algorithms, developed for stochastic processes, that will navigate the landscapes to yield defect-free products. This strategy will be demonstrated and refined on prototype lab-scale reactors, using real-time digital microscopic imaging as the sensor and programmable particle-particle interaction potentials & electric fields as the actuators, to produce meta-materials.

In terms of broader impact, successful development of fundamental tools for large-scale assembly of defect-free colloidal crystals has the potential to produce revolutionary technologies (e.g. optical computing, energy harvesting, sub-diffraction limit imaging, invisibility cloaking) not unlike the creation of single crystal silicon to enable integrated circuits and modern computing. No existing processes today are capable of producing such materials at a commercial scale despite 25 years of trial-and-error efforts. A strategy of rigorous real-time control using quantitatively accurate process models, like that proposed here, is required. The education and outreach activities will incorporate integrate concepts from modeling, control, simulations, and experiments, including rich visual data from colloid experiments (e.g. images, videos) and physics-based simulations (e.g. renderings, animations) to provide intuitive education/training for students at all levels.

1403542
Ford
UMass Amherst

Mesoporous inorganic membranes, composed of materials such as silica and alumina and having pore sizes on the order of 2 to 50 nanometers, have significant potential for performing separations of mixtures of small molecules. Important examples include the removal of carbon dioxide from flue gases and the recovery of ethanol from fermentation broths. Chemists and materials scientists now have an amazing amount of control over the geometry and surface chemistry of the pores when synthesizing mesoporous inorganic membranes. However, actually knowing what pore geometry and chemistry to choose for a given separation remains an outstanding problem, partially due to the lack of appropriate models that connect detailed material structure to membrane flow rates.

In this project, a new modeling approach is proposed to capture the complex adsorption and flow mechanisms that take place inside the membrane pores during separation operations. The modeling, based dynamic mean field theory (DMFT), retains molecular-level detail while predicting membrane performance at the laboratory or industrial scale. A combined program of theoretical development, computer simulation, materials synthesis, and permeation measurement will develop DMFT into a tool that chemists and materials scientists can use to guide the manufacture of new membranes, and engineers can use to model the performance of industrial membrane units. A novel class of mesoporous membrane materials will also be developed as a key part of the project.

The PIs propose a collaborative theoretical/experimental research program that will transform the modeling of separations with mesoporous inorganic membranes through the further development and DMFT. DMFT has had an enormous impact on the closely related application of adsorption in mesoporous materials. With some further development to the dynamic aspects of the theory, DMFT msy also meet the challenge of predicting permeation through mesoporous membranes. The research team for this project spans molecular theory and modeling (Ford, Monson), membrane science and technology (Ford) and the materials science and engineering of mesoporous materials (Fan, Monson).

The intellectual merit of this proposal lies in two main objectives. The first is to extend and develop dynamic mean field theory (DMFT) for quantitatively accurate prediction of permeation of small molecules in mesoporous membranes. This is proposed to be accomplished by (i) establishing the method on lower-dimensional, geometrically simple pore models; and (ii) modifying the dynamics to quantitatively capture relevant transport mechanisms. The second major objective is to apply DMFT to model specific mesoporous membrane permeation experiments. This will be accomplished by (i) synthesizing a set of membranes with controlled pore size and geometry; (ii) comparing DMFT predictions to separation experiments on these membranes; and (iii) using DMFT to improve the accuracy of pore sizes obtained by permporometry, which uses co-permeation of a light gas and a condensable vapor to gain information about pore size.

If successful, the products of this research have the potential to advance the membrane industry in the U.S., especially as it is applied to the traditional and emerging fields of energy production. The proposed work may bridge the statistical thermodynamics, adsorption, and membrane communities while providing the membrane community with a new computational tool for predicting and interpreting permeation through mesoporous membranes. The PIs propose to integrate the research into the undergraduate and graduate curricula at UMass Amherst, through a popular undergraduate nanomaterials elective taught by one of the PIs (Fan) and a core graduate course in statistical thermodynamics taught by one of the other PIs (Ford or Monson). Existing outreach and recruitment programs at UMASS will also be leveraged.

This Designing Materials to Revolutionize and Engineer our Future (DMREF) collaborative research project will use a combination of theory, numerical simulation, and experiment to discover and synthesize new crystalline materials that can enable the manufacturing of metamaterials. Metamaterials have unique periodic structures that can be used to manipulate electromagnetic or mechanical energy. The materials will be formed from the self-assembly of colloidal particles in suspension. This route to metamaterials is especially flexible, because many kinds of interactions among the particles can be exploited to form new crystalline materials. In addition, it allows better control over the formation process, which can reduce defects in the resulting crystalline structures. The results of the project will provide scientists and engineers with improved tools for identifying colloidal systems of interest, predicting stable crystalline structures, and guiding synthesis of the new materials.

Theory, simulation, and experiments will be integrated into a program to design systems of colloidal particles that assembly into desired crystalline structures. New theoretical and simulation methods will be developed to predict stable and metastable crystal structures in colloidal systems, with a focus on enhancing capabilities of classical density functional theory and applying hyper-parallel tempering simulation methods. Experimental tools for measuring and designing colloidal potentials and analyzing crystal structures will be extended to binary mixtures. The focus will be on developing and measuring suitable potentials for binary systems through the use of different particle sizes and materials, doublets/dumbbells, and Janus configurations, and on characterizing crystal structures using advanced confocal microscopy techniques. The results will be used to design colloidal systems that assemble into desired crystalline structures. Three specific platforms to be considered are solid-fluid and solid-solid polymorphic transitions in binary mixtures of spherical particles of different size and interaction potential, plastic to close-packed solid transitions for doublet/dumbbell particles, and the formation of non-close-packed structures for particles with orientation-dependent attraction (Janus).

The scholarship program in the College of Engineering at the University of Massachusetts Amherst will increase the number of community college students with demonstrated academic talent and financial need who transfer, complete baccalaureate degrees in engineering, and enter the STEM workforce. The project will begin with the recruitment of a group of 22 new community college transfer students. The selected students, to be known as S-STEM Scholars, will receive up to $6,000 per year in scholarships and participate in a comprehensive program of academic, professional and personal support. Nearly half of the students who earn baccalaureate degrees in science and engineering in the US complete part of their education at a community college. Programs designed to support community college students to transition to, and graduate from, four-year engineering programs will increase the number of engineering graduates entering the workforce. Scholarships for academically strong engineering students, who may not otherwise be able to afford college, will increase the number of engineering graduates prepared to promote innovation and competiveness in national and regional technology-intensive industries.

The enrichment and support programs build upon effective practices known to help increase retention and degree completion among community college students that transfer to four-year baccalaureate degree programs. The program will include activities to promote faculty-student interaction, offer both peer-to-peer and industry mentoring through a Connect for Success Mentoring Network, provide several workshops focused on academic success, and deliver a suite of career development workshops customized for the S-STEM Scholars. This program design will help to overcome known barriers to persistence of transfer students from community college. These barriers are lack of engagement on campus, underdeveloped professional identity and career goals, incomplete study habits, fewer opportunities to gain practical competence, and the need to earn money through non-academically related work. Assessment and evaluation will provide insight into the retention benefits of student scholarships, learning communities, career development activities, and faculty mentoring/advising. Lessons learned and effective practices that emerge from the program evaluation data will be disseminated widely to the engineering education community and help enlarge the knowledge base regarding attributes and practices of successful scholarship programs of this type.